We propose to continue our quest for the identification of antigens primarily involved in the autoimmune diabetes of the NOD mouse. We have an NIH supported grant that examines the biochemical role of the class II MHC molecule I-A(g7) .This is a complementary project that seeks to identify the antigens that are targetted for immune recognition at an early stage of the diabetic process of the mouse. There is the likelihood that many protein antigens are involved in diabetes, some of which may be major in initiating disease, while others may have no pathogenic significance. Our task is to identify which are significant and causally related to pathology and which are irrelevant. Our strategy here is to examine the initial B cells that are activated at the start of the process. The early serum antibodies of the IgG class indicates the selection by beta cell derived antigens of clonal B cells that receive CD4 T helper cell-derived signals for immunoglobulin class switch. The implication is that the cloned B cell must have presented MHC-bound peptides derived from the processing of the protein antigen. We propose to biochemically identify the protein antigen by producing monoclonal antibodies. (We have already produced several clones and selected some for our initial analysis. We believe the use of the monoclonal antibody will greatly facilitate the chemical analysis.) We propose to search for the complementary CD4 T cells in lymph nodes and to identify them, determine the peptides that are recognized and, importantly, establish their diabetogenic potential by functional assays in which the cells are transferred to NOD.SCID mice. We propose experiments to determine which APC is presenting antigens and where; and the role of B cell as an antigen-selecting APC based on the selective advantage of antibody specific receptors. Importantly, the causal relationship between the antigen and diabetogenesis will be evaluated. We have the infrastructure and experience to carry out the biochemical and cellular experiments. We present the initial results that identify an early antigen, a retrovirus env protein expressed in beta cells. The CD4 T cells that recognize an env peptide have now been identified and are being tested for their pathogenicity.